A known valve operating mechanism is used, for example, as an air intake valve operating mechanism in which the intake valve is formed at an intake manifold of a vehicle. The air intake valve is supported at an intake passage so as to be able to open and close. The air intake valve changes an air intake flow rate by opening and closing to thereby improve engine combustion.
Such air intake valve operating mechanism is disclosed in JP05-069474U. The operating mechanism disclosed includes a valve body (valve) provided at an air intake pipe, a shaft body supporting the valve body so as to be integrally rotatable therewith, and a link member. The link member is connected to the shaft body so as to be integrally rotatable therewith. The link member is also rotatably connected to an actuator rod that performs a protruding operation and a returning operation relative to an actuator. As a result, the protruding operation and the returning operation of the actuator rod are transmitted as a rotational operation to the valve body so that the valve body opens and closes. The valve operating mechanism is required to appropriately adjust an opening degree of the valve body in response to a condition of the engine revolutions, and the like. Then, in order to prevent looseness at a connecting portion between the actuator rod and the link member, a torsion spring is provided. One end of the torsion spring engages with the link member while the other end of the torsion spring engages with an actuator bracket through which the actuator is fixed to an outer peripheral portion of an intake manifold. The link member and the actuator rod are biased by the torsion spring so as to contact each other to thereby prevent looseness at the connecting portion between the actuator rod and the link member.
According to the valve operating mechanism disclosed in JP05-069474U, however, the torsion spring is disposed between the link member that is movable and the actuator bracket that is fixed. Thus, at the time of operation of the actuator so as to operate the link member via the actuator rod, the actuator needs to operate against a biasing force of the torsion spring. As a result, a large-sized actuator is required to achieve a desired responsiveness for opening and closing of the valve.
Thus, a need exists for a valve operating mechanism which is not susceptible to the drawback mentioned above.